ABSTRACT Zooplankton exhibit several trends of variation in space and time, and these trends can be more evident in natural environments without anthropic perturbations. Examples of anthropic factors are climate change, eutrophication and construction of reservoirs. This study evaluated the influence of three factors - seasonality, type of environment and the presence of aquatic macrophytes - on various ecological attributes of rotifers in a river-lake system located in the Paraná River floodplain. Monthly samplings were conducted during 1993 and 1994. The mean species richness per sample was 60 species. The seasonality and the type of environment influenced the ecological attributes of rotifer assemblages, while the presence or absence of aquatic...

Bacteria associated with semi-continuous culture of Brachionus plicatilis , which is used as the first food of marine fish larvae, were counted on Zobell 2216 E medium and identified. The numbers of bacteria were very high in both Brachionus (about 10 super(11) bact. per ml of digestive content) and in water (from 1.6.10 super(6) to 4.7.10 super(7) bact. per ml). The cultures were studied at driving a time when mortalities occurred frequently. The introduction of a Pseudomonas) phenon at a proportion of about 50% to the dominant microflora persisted in time and was little influenced by diet. It has been the cause of the repression of the Vibrio, Aeromonas group which was found in an unusually small proportion. It induced a lack of microflora diversity and...

Live foods such rotifers and Artemia are still indispensable for mass propagation of larval fish. At present, more than 20 fish and crustacean species are mass produced in Japanese governmental fish farming centres and private hatcheries. Fry are either released into the coastal areas or used for commercial cultivation. This culture technology is rapidly developing with new species being introduced each year and larval rearing is increasingly identified as the number one constraint. Artemia is used most extensively, particularly for the mass production of Kuruma prawn, Penaeus japonicus .

Rotifers were reared on the artificial diet culture Selco® in batch and recirculation conditions at different water exchange rates. The different rearing conditions resulted in considerable changes in water quality, which in their turn affected rotifer growth and food consumption. At a daily water exchange rate of 100%, no positive effect was obtained in rotifer growth compared to the batch rearing system, but the rotifer culture period could be prolonged by 1 week. By increasing the daily water exchange rate from 100 to 300% the maximum rotifer density could be significantly (<i>P</i> < 0.05) increased from 1800 to 2500 individuals ml<sup>-1</sup>. At the highest recirculation rate (daily water exchange of 500%) the highest...

A chytrid fungus Olpidium gregarium was found in Rio Grande Reservoir as rotifers populations' parasite. Along the reservoir central axis, the rotifers density decreased in the dam direction, while the density of affected rotifers by the chytrid fungus increased in the same direction. Moreover, some rotifers species were more affected than others, thus showing certain preference for some rotifers species. Thereby, this parasite may be interfering in the distribution of rotifers population in Rio Grande Reservoir. This is the first report of this species for Brazil.

The dynamics of resting egg production of the rotifer <i>Brachionus plicatilis</i> originating from a wild population in the Tanggu Saltworks (P.R. China) was investigated. In the natural environment as well as in semi-controlled rearing conditions an increased resting egg production was noticed with declining food availability. Processed resting eggs had a hatching efficiency of 3x10<sup>6</sup> rotifers per gramme irrespective of their origin. Hatching started 22h after the initiation of incubation and was completed after 36h. Rotifers obtained from resting eggs could be further cultured on Culture Selco® and enriched with Super Selco®. The fatty acid profile of these rotifers were not divergent from reference rotifers...

ABSTRACT Richness estimators (Jackknife 1, Bootstrap, Chao 1 and ACE) were used to relate zooplankton species richness with amount of water collected per sample and number of samples throughout the year for the limnetic region of Sapucai River compartment of Furnas reservoir, state of Minas Gerais, Brazil. Seven 100 L samples were collected in sequence using a motor pump, and seven 70 L samples were collected in sequence using a plankton net (68 μm mesh size) in vertical hauls, to totalize 450 L, in three stations of the reservoir. Twelve monthly samplings were carried out over a year. The assessment of richness was made by analyzing the asymptotic behavior of the estimator curves. The samplings reached the asymptote from 350 L of collection with trawls...

The mahimahi, Coryphaena hippurus , has excellent potential for aquaculture due to its fast growth (2 kg at 6 months, 9 kg at 1 year), good food conversion efficiency (30%, wet weight), high fecundity with natural captive spawns (200,000 eggs/female/2 days year round for a 1 year old female), and high price (US$ 9.00/kg wholesale in Hawaii).

The effect of bacterial strains on the growth rate of rotifers, Brachionus plicatilis, was determined under monoxenic conditions. The first objective was to obtain sterile rotifer cultures starting from rotifer resting eggs using merthiolate or glutaraldehyde as disinfectant. Sterile rotifer cultures were obtained, without affecting the hatching ability of the resting eggs, when 0.05 µl/l glutaraldehyde was used. This disinfection procedure was used to examine the effect of 20 bacterial strains, isolated from well-performing live-feed production systems, on the population growth rate of rotifers cultured under monoxenic conditions. Five out of the 20 bacterial strains tested were able to improve significantly the asexual reproduction of rotifers. The...

Abstract ? The objective of this work was to determine seasonal variation and vertical distribution of the soil rotifer assemblage in a climax beech forest in South Bohemia. During 2005, soil rotifer was investigated to the species level. Soil samples of 10 cm2 and 10 cm in depth were divided into five layers, which were processed separately. Thirty one rotifer species were identified during the investigation. Dominant species significantly changed throughout the seasons. The most abundant species were Encentrum arvicola and Wierzejskiella vagneri among the monogononts, and Adineta steineri, Ceratotrocha cornigera, Habrotrocha filum, Habrotrocha ligula, Macrotrachela plicata, Mniobia tentans, Mniobia incrassata and Mniobia granulosa among the bdelloids....

The objective of this work was to determine seasonal variation and vertical distribution of the soil rotifer assemblage in a climax beech forest in South Bohemia. During 2005, soil rotifer was investigated to the species level. Soil samples of 10 cm² and 10 cm in depth were divided into five layers, which were processed separately. Thirty one rotifer species were identified during the investigation. Dominant species significantly changed throughout the seasons. The most abundant species were Encentrum arvicola and Wierzejskiella vagneri among the monogononts, and Adineta steineri, Ceratotrocha cornigera, Habrotrocha filum, Habrotrocha ligula, Macrotrachela plicata, Mniobia tentans, Mniobia incrassata and Mniobia granulosa among the bdelloids. Mean Shannon...

The purpose of this study was to describe the composition and abundance of rotifers in different environments: one lotie (the Ivinheima River) and another lentic (the Patos Lake) located in the floodplain of the Upper Paraná River. The influence of limnological variables on the structure and dynamics of rotifers was also examined. Samples were taken monthly from March 1992 through February 1993, in the open water region of the lake and river and in the channel between them and, in the littoral region of the lake and river. Of the 96 species identified, the best represented families were: Brachionidae (20 species), Lecanidae (18 species), and Trichocercidae (15 species). 55 species were widely distributed, 13 were pantropical, 16 neotropical (8 endemic to...

The efficiency of different methods for the purification and maintenance of axenic cultures of a rotifer and an unicellular alga is tested. The use of antibiotics seems to be the most suitable method to realize bacteria-free cultures of plankton. No elements prove that the presence of bacteria is necessary for the development of the cultures. Bacteria-free cultures show a physiological evolution of the culture medium is enriched with some nutrients.

Newly-hatched grouper larvae were reared for 24 days at a density of 15 larvae.l<sup>-1</sup> in 250-l capacity cylindro-conical tanks filled with 200l seawater. Starting day 2, the larvae were given: <i>Chlorella</i>-fed rotifers (Chl-R) rotifers fed Culture Selco (INVE Aquaculture NV, Belgium) (CS-R), and rotifers fed Culture Selco and consequently enriched for 24h with 20% vitamin C (CSC-R). The rotifer density in the larval tanks was maintained at 15 rotifers.ml<sup>-1</sup>. The rotifer diet was supplemented with egg yolk until day 5. Each treatment had five replicates. Preliminary results show no significant difference in the survival rate of grouper larvae given Chl-R (4.21±2.8%), CS-R (2.56±0.9%) and CSC-R...

Rotifers have often been used as indicators of sudden changes in physical and chemical features of the aquatic environment. Such features vary greatly during flood pulse events in small lakes connected to major floodplains. However, few are the studies that investigate the consequences of the flood pulse in rotifer species composition, abundance, richness and diversity, especially in Amazonian lakes. We analyzed samples from a small blackwater lake of an “igarapé” connected permanently to the Negro river, in Central Amazonia. Samples were taken twice a year for two years, comprising flooding and receding periods of the flood pulse. Rotifer abundance increased significantly after draught events, and electrical conductivity and turbidity were intrinsically...

Seasonal fluctuations in the dynamics of the plankton rotifer populations in an oligo-mesotrophic branch of a tropical reservoir were analyzed with respect to the possible influence of environmental conditions (physical, chemical and biological), with emphasis on biological interactions. Samples were taken monthly from August 2006 to July 2007. The well-defined climatic seasons were reflected in variations of the physical and chemical properties of the water. The zooplankton community consisted mainly of Rotifera, Cladocera and Copepoda, with occasional representatives of Chaoborus brasiliensis (Diptera), Ostracoda, Protozoa and Turbellaria. Rotifera was the dominant group in zooplankton community in 5 of the 12 months of the study and were represented by...

In this study, 4 rapid (90 min) toxicity tests were developed using ingestion and digestive enzyme activity of <i>Daphnia magna</i> juveniles. Ingestion activity was assessed using fluorescent labelled latex micro-beads and digestive enzyme activity (trypsin, beta-galactosidase and esterase) was measured in homogenates using chromogenic (N-benzoyl-L-arginine-4-nitroanilide) and fluorogenic (4-methylumbelliferyl-B-D-galactoside and fluorescein diacetate) substrates.All assays and toxicity endpoints were evaluated for their potential use as routine toxicity testing tools for pure chemicals and sediment pore waters. The observed high correlation coefficients (r(2)>0.9) between the short-term toxicity values and the acute toxicity endpoint (24h...